Light has profound influences on many non-image forming (NIF) visual functions including circadian rhythms, sleep, mood, body temperature and the pupillary light reflex. In mammals, light influences these NIF functions through three retinal photoreceptors, namely the classical photoreceptors, rods and cones, and the intrinsically photosensitive retinal ganglion cells (ipRGCs), which express the photopigment melanopsin. As ganglion cells, ipRGCs integrate rod/cone input with their own intrinsic melanopsin-based phototransduction to serve as the sole conduits to signal light information to brain regions important for these NIF functions. However, how ipRGCs, a seemingly homogeneous population, integrate extrinsic light input from rods and cones with their own intrinsic melanopsin-based light responses to coordinate diverse behaviors is poorly understood. The overall goal of this competitive renewal is to address this fundamental question at three levels. In Aim I, we will determine the functional circuits by which rod, cone and melanopsin-based signals are integrated in ipRGCs to drive NIF functions. Recently, we found that ipRGCs are much more diverse than previously appreciated, consisting of multiple morphologically and electrophysiologically distinct subtypes. Additionally, ipRGCs appear to be unique among retinal ganglion cells in that they co-express two neurotransmitters, glutamate and a neuropeptide, PACAP. Thus, in Aim II, we will define the relative contribution of glutamatergic and peptidergic neurotransmission to diverse NIF functions. In Aim III, we will elucidate the functional contribution of individual ipRGC subtypes to NIF functions. These studies will advance our current understanding of the role of ipRGCs in controlling light- mediated behaviors that are essential to human health and a better quality of life.